Calibration of laboratory aging practice to replicate changes to roof albedo in a Chinese city

Highly reflective roofs can save building air conditioning energy, mitigate the urban heat island, and offset CO₂ emissions. A laboratory aging methodology was developed to simulate change in the solar reflectances of field-applied roof coatings induced by one year of natural exposure in Guangzhou (China). The approach compared the changes in solar reflectance spectra observed in the naturally exposed materials with those obtained following a three-stage laboratory procedure: conditioning, soiling, and weathering. The method was systematically modified over five trials by adjusting the key variables in laboratory aging: composition of the soiling mixture, deposition mass, and conditions of soiling application. Tests were performed using a small number of specimens. Simulating exposure in Guangzhou required a loading of soiling agents greater than that used to simulate US cites. In the final trial, the reduction in solar reflectance was reproduced to within an average of 0.02 for three of the six products, and to within an average of 0.06 for the remaining three products.